The present invention relates to a method and an apparatus which enable the picking frequency of pile wire looms to be increased. The present invention relates more particularly to looms for weaving fabrics which have a pile loop every n wefts, n being greater than or equal to two.
Pile wire looms are provided with one or more devices which during weaving insert pile wires into the shed in such a manner that the wires come to lie on the ground texture and that the pile warp threads forming the pile pass over the pile wires and thus form pile loops. The same devices withdraw the inserted wires out of the fabric formed, so that pile loops or tufts are left behind on the fabric. If the pile wires are provided with small cutters at their ends, the loops are cut through so that an upstanding pile is left on the fabric.
In the weaving of fabrics having a minimum of one pile loop every n wefts, one pile wire must be inserted into the shed every n wefts. For the two-weft V weave, for example, one pile wire must be inserted every two wefts. The classic pile wire cycle in the weaving of a fabric with a weave of this kind is as follows. A pile wire is extracted during the weft cycle m and inserted during the following weft cycle m+1. For this purpose the pile wire insertion and extraction device is provided with one pile wire carriage, which during the weft cycle m extracts a pile wire and during the following weft cycle m+1 inserts the same pile wire.
The picking frequency or speed of revolution of pile wire looms of this kind is limited by the heating-up of the pile wires during their extraction. The heat produced is caused on the one hand by friction between the pile wire and the pile threads surrounding it, and on the other hand, in the case of cutter pile wires, through the cutting of the pile loops. Particularly in the latter case, the heat produced is difficult to dissipate because it is highly localized, occurring at the cutting edge of the cutter. The local temperature can then easily rise above the discoloration point of the pile threads, so that they are damaged. This is naturally unacceptable, so that the speed of extraction of the pile wires must be kept within certain limits. Another hindrance is the so-called "transfer" time. The "transfer" time is the time required between weft cycle m and weft cycle m+1, around the beating-up by the reed, for re-orienting the pile wire extracted during the weft cycle m to bring it from its extraction position to its position for insertion into the shed. The extraction time is thus shorter than the time between two operations of the reed. It is thus clear that, in view of the limited extraction time and the limited speed of extraction, the picking frequency is also restricted and that the greater the width of the fabric, or the distance over which the pile wires have to be extracted, the lower the picking frequency will be.
The use of lubricants, the blowing of cold air over the pile wires, and the increasing of the number of pile wires in the fabric--the so-called pile wire packet--are known means for overcoming this problem, but these means bring about only a very slight reduction of the limitation of extraction speed.
In BE 893,051 a solution to this problem is disclosed, consisting of a method whereby two or more pile wires are extracted at the same time from the fabric. The simultaneous extraction of pile wires, however, gives rise to a number of fundamental problems and disadvantages. If a plurality of pile wires have to be extracted simultaneously on one side of a loom, a complicated extraction, transfer and insertion device is necessary. No device of this kind is known up to the present time, and the publication mentioned is also vague on this subject. The publication mentioned in fact describes only one valid device for applying this method. This device consists of two pile wire operating devices, which are installed separately one on each side of the loom. However, this arrangement has the great disadvantage of requiring a width three to four times that of the maximum width of fabric, which is extremely space consuming. In addition, this arrangement has the disadvantage that provision must be made to coordinate the movements of the two pile wire operating devices. This entails the incidental provision of mechanical transmission or electronic control for both the pile wire operating devices. The publication mentioned suggests that this arrangement makes it possible for a pile wire to be extracted over three picking periods, so that the pile wires are thus extracted at one third the speed reached with the classic method. This assertion is however incorrect, because it does not take into account the time needed for bringing the extracted pile wire from its extraction position to its insertion position.